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1. Field of the Invention
The present invention relates generally to efficient control of thrust vectors for jet and turbo jet engines and the actuation of their control surfaces.
2. Prior Art
Thrust vector control of propulsive jet engine exhaust is desirable for a variety of applications including emergency safety steering control, reducing G force loads on aircraft control surfaces, enabling higher G turn capabilities for aircraft, optimizing engine thrust, fuel economy and thrust response time and for application in engines used in aircraft design to hover or execute vertical takeoff and landing or very short takeoff and landing. Currently available thrust vector control systems provide only coarse control. In order to provide fine control of current thrust vector controllers, auxiliary systems are necessary. These systems typically involve smaller thrusting devices remote from the main engine exhaust. Consequently, complex and expensive ducts, reservoirs, pumps and the like are required. The complexity of these systems decrease reliability and durability while increasing expense. Thrust vector control for jet propulsion of all kinds of aircraft has a constant need for increasing economy, durability, reliability and safety.
Even the coarse control currently available with current thrust vector control systems typically involves overlapping vanes or plates which generate a high amount of friction with one another and/or their housings in operation. Hence even for coarse control a high actuation force is required. High actuation force again requires a complex and expensive system of hydraulic or mechanical actuators. Both these systems and auxiliary fine vector thrust control systems present risks of fire, inoperability and engine contamination in case of leaks or other failures. When high force is required at high thrust levels, present systems are not always capable of providing the required actuation force under all conditions, especially low speed applications such as VTOL.
The expense and complexity of the currently available actuation systems make retrofitting thrust vector control systems onto existing jet engines impractical and expensive. As lighter and cheaper jet engines are brought to market for applications with smaller aircraft, affordable and reliable retrofitting systems become attractive. Moreover, the availability of retrofitting capabilities is desirable for use of thrust vector controllers as an emergency safety system.
The present invention is a multi-lobed, low friction vane thrust vector controller for jet propulsion engines. A housing is disposed around a jet engine exhaust. The housing has four brackets, aligned in perpendicular opposing pairs. In each bracket a curved vane is pivotally installed. The vanes may be pivoted inward to restrict or outward to open exhaust flow through each bracket. The vanes are independently controllable. Accordingly, the vanes may be pivoted inward to constrict exhaust flow in an individual bracket, or in any combination of multiple brackets. By selectively constricting the flow of propulsive exhaust gas in the four brackets, the engine thrust vectors may be controlled. The amount of thrust vectoring is controlled by the degree to which a vane is pivoted.
Each vane has an independent actuator. The actuator is powered by bleed air from the main chamber of the jet engine. Bleed air is shunted into a sealed cylinder having a piston in it. The path of the incoming air is down an axial shaft, out a port in the piston between the edge of the piston and the wall of the cylinder and then into chambers on either side of the piston. The piston is fixed to a piston rod which extends from the cylinder to its pivotal attachment with the vanes it actuates. Hence, movement of the piston in one direction pushes the connected vane into the exhaust thrust and movement of the piston the other direction withdraws the vane from the exhaust thrust.
The constant flow of air through all parts of the cylinder cools it. This allows for a compact design, since a self-cooled piston and cylinder actuator may be placed close to the jet combustion chamber without the need for expensive high temperature bearings or the risk of temperature related degradation.
The direction of piston and piston rod travel is controllable through a pair of control ports in the piston shaft. One control port connects the hollow piston rod air exhaust with a first chamber on one side of the piston and the other port connects the hollow piston rod air exhaust with a second chamber on the other side of the piston. A valve coaxial with the piston rod and traveling through its hollow shaft selectively opens one or the other control port. By opening one or the other port, air pressure is increased in one chamber and decreased in the other, driving the piston to move towards the low-pressured chamber. The piston rod moves with the piston and actuates the vane.
Only a small amount of force is necessary to close one control port and open the other because of the actuator cylinder""s use of dynamically opposing air pressure chambers. Movement of the piston is initiated by a control port selection valve connected to a shaft. The valve shaft runs from the valve within the piston/piston rod assembly and out to a housing where it is connected to a gear rack. Through a pinion gear a servo motor drives the gear rack and valve shaft to move the control port selector valve between the pressure control ports. An ordinary electric motor operated by a 12-volt battery is sufficient.
Through the independent control of thrust vector control vanes in the described manner, the present invention is capable of inexpensive, robust, reliable, and retrofitable control of pitch, yaw, and roll. It can optimize thrust, thrust response time, and fuel economy for various altitudes and speeds. It is useful for applications as an emergency back up steering system, and for short takeoff and landing and vertical takeoff and landing applications, especially those requiring hover control.
Further features and advantages of the present invention, as well as the structure and operation of various embodiments of the present invention, are described in detail below with reference to the accompanying drawings.